Composting Toilets

I happen to be writing an article this month about my experience with designing a composting toilet facility for a nature preserve in southern Kentucky. So let me take a few minutes to summarize (sorry – it is long): Toilet systems that use water to carry the waste product away have recently come under scrutiny due to concerns about availability of water. This is of greater concern in the arid west, but all may be subject to some cost of treatment of the effluent. There are two primary wet systems: connected into a municipal sewer or a septic system. For a septic system, one must be concerned about percolation rates AND the depth to the groundwater. In Kentucky there is a lot of porous limestone, fairly near the surface (i.e. Mammoth Cave). If the bacteria and microbes haven’t finished their job by the time the liquid seeps into the groundwater, your neighbors downstream will not be happy.

Dry systems are worth considering. Pit type outhouses are the oldest “system”. They are inexpensive because they are temporary. After a while that pit will fill up. You can move the whole structure or build new. Plus there is the potential for leaching contaminants into the groundwater. And in the heat of the summer there is an odor. There are Incinerating toilets. Very compact, but they require gas or electricity to operate. A little bit of ashes need to be removed occasionally. Most of these are very small and appropriate for a cabin in the woods – not heavy use. Composting systems seemed tome to be the best choice for my project of all the dry systems. (You may know this already but.) when a bear shits in the woods, there are organisms and microorganisms in the leaf litter and top layer of the soil which break down the animal wastes into nutrients for the plants. Composters require an initial inoculation of microorganisms and a layer of wood shavings to take the place of the leaf litter. After each use another scoop of wood shavings is added. After some period of time, the decomposers happily turn what we consider waste matter into the same type of compost that you can get from the community scrap food pile next to the vegetable garden. And anyone who has messed with the compost pile knows that there is an optimal ratio of autumn leaves, grass clippings, vegetable scraps, eggshells and water to get the proper nitrogen-carbon mix. There are choices among composting systems – large scale use and small scale like in a home. They all use wood shavings to provide the plant matter component and there must be some space below the toilet for the composting to occur (frequently downstairs). Most of the small scale systems are homemade, and therefore less expensive, but also subject to being more finicky.

One system is called “Owner built 2 chamber”. Downstairs there must be two miniature rooms (chambers) side by side, with access doors in a front wall. Upstairs is a large toilet room over the top of both chambers with a hole in the floor. The toilet is secured over one hole while the one chamber is accepting contributions. The other hole is closed off. When the first chamber is full, switch the toilet over to the other side and contribute to the second side, letting the material in the first chamber decompose. There needs to be a vent pipe for each chamber and a convenient container of wood shavings proximate to the toilet. The floor of the chambers needs to pitch in one direction to collect excess liquid. This can be piped out to a graywater bed that has other water sources contributing to it (i.e.laundry).
Another system is called the “Carousel”. At one time they could be purchased from Scandinavia, but I think these days one must construct their own based on that design. There is a rotating drum divided into quadrants. The center of the drum is offset from the toilet chute above so the contributions go into one quarter. When that quadrant is full, rotate the drum and contribute to the next space. By the time three quadrants are filled, the material in the first quadrant is composted, and it can be removed to the garden or landscaping.

The final homemade system I will describe is the “Big Batch – EKAT”. This relies on two (or more) wheely bins, or demolition carts that have a sinuous sculpture of perforated pvc pipes for ventilation – which must be connected to a vent pipe. One receives the contributions while the other is processing. And once it is ready to be emptied, take it straight out to the garden.

For my project, I didn’t think our volunteers would be willing to deal with any of the homemade systems, and I didn’t think they had the necessary capacity, so I went up in scale to the pre-engineered, manufactured systems. One big advantage is that they are more likely to be accepted by regulatory authorities like Health Departments. All these require a vent pipe which takes away the odor, sometimes fan assisted which requires electricity – either from the grid or from a Photo Voltaic panel. There also must be a method to collect & remove excess liquid. This can be either with an evaporation chamber or into a graywater garden. Depending upon your usage (liquid contributions vs solids) and your ambient humidity, there may be a need for additional water into the composter. Someone else mentioned Clivus Multrum. They have been around a long time, make good quality systems, spend a lot on advertising and continuing education which contributes to a higher cost. I think another aspect is they are located in the northeast (higher land cost and higher employee pay). Definitely worth looking at their products! I chose the Phoenix 200 system from Advanced Composting in Whitefish, Montana. Their unit is more vertical than the Clivus, and has a slightly different way of moving the material down to the removal door. Cost of unit was 75% of the big brand name.

There are at least two other large scale systems manufacturers. One is Composting Toilet Systems in Newport, Washington. I can’t find my records on the other, but it is also closer to the Pacific Ocean. Their systems are similar in design to the Clivus Multrum base line model. I’m not sure of the costs of these, since the footprint of their composters did not fit my design as well as the Phoenix. My design has been in operation for almost two years, and amazingly the compost is not ready to be removed. We keep adding shavings and the level doesn’t rise. I don’t know what is going on, but it is not a problem, so I will let the microorganisms keep doing their thing. Well, that is enough for today. Search the internet for “composting toilet systems” and you will find plenty of additional reading.

Neena Jud, AIA LEED AP
Harmony Architecture
Cincinnati, Ohioharmony [at] one [dot] net

Category: Green Building

Tags: Design

Views: 583

Related Posts Cohousing Blog